1. Technical Field
This application relates to an optical cable, which can be used for blowing into an empty tube, and to a method for the production of an optical cable which can be used for blowing into an empty tube.
2. Technical Background
To set up access networks, telecommunications operators usually use optical cables which are blown into thin, preinstalled empty tubes made from a plastics material. Used in particular as such optical cables are so-called micromodule cables, in which the cable core is formed without any filling compound or is filled with a gel.
FIG. 1 shows a so-called dry micromodule cable with a cable core 100 without any filling compound. The cable core has a centrally arranged yarn 20 of polyester, arranged around which are several optical transmission elements 10, which are formed as so-called micromodules. A micromodule comprises several optic fibers 1, which are surrounded by a sleeve 2 made from a plastics material. The centrally arranged filament 20 contains a swellable material, which on contact with water brings about an increase in volume of the filament 20.
Furthermore, the cable core 100 is surrounded by a strip 400 formed into a sleeve. The sleeve 400 has a multilayered structure of polyester yarns. Between individual layers of the polyester fabric there is a swellable SAP (super absorbent polymer) material.
When water penetrates into the cable core 100, the SAP materials bring about swelling of the sleeve 400 and swelling of the filament 20. This prevents water that is inside the cable core 100 from spreading along the optical transmission elements 10, thereby preventing deterioration of the optical transmission properties.
Arranged over the sleeve 400 is a cable jacket 300. Apart from the function of preventing the spreading of water along the optical transmission elements in the cable core, the sleeve 400 protects the optical transmission elements 10 from high temperatures that occur during the extrusion of the jacket.
Apart from the dry embodiment of a micromodule cable that is shown in FIG. 1, micromodule cables in which the cable core is filled with a gel also exist. In the case of this type of cable, the gel which surrounds the optical transmission elements 10 prevents water from spreading along the micromodules 10 if there is any moisture penetration.
After a micromodule cable has been blown into an empty tube, the individual optic fibers of the micromodule cable are spliced with optic fibers of another micromodule cable or with some other item of hardwire. The cable ends of the micromodule cable must be suitably prepared for connection to the hardware. To expose the optic fibers, firstly the cable jacket is removed. After that, the cable core of the micromodule cable is also surrounded by the polyester fabric of the sleeve 400. The sleeve 400 is generally removed by cutting off the fabric with a cutting tool. In the case of an optical cable filled with gel, in a next step the exposed optic fibers are cleaned of the gel with a solution.
In the case of a dry micromodule cable, there is no need for gel to be cleaned from the optic fibers to be spliced, so that in the case of this type of cable it is already possible to save time for the preparation of the micromodule cable for the splicing operation. However, it may still be necessary after removal of the cable jacket to remove the swellable sleeve 400 with a knife or scissors. Apart from the time required for this, cutting off the sleeve 400 always also entails a risk of damaging the optic fibers.
The object of the present invention is to specify an optical cable that has good processing characteristics in the preparation of the optical cable for a splicing operation. A further object of the present invention is to specify a method for the production of an optical cable that has good processing characteristics in the preparation of the optical cable for a splicing operation.
The object with respect to the optical cable is achieved by an optical cable with a cable core with several optical transmission elements, which contain at least one optic fiber, with a first sleeve made from a material containing paper, the first sleeve surrounding the several optical transmission elements, with at least one yarn, which is arranged in a region of the cable core between the first sleeve and the several optical transmission elements, the at least one yarn comprising a swellable material, and with a cable jacket, which surrounds the first sleeve and contains a plastics material.
According to a development of the optical cable, the paper has a tear strength which is less than 16 N/mm2. In a preferred embodiment, the paper has a tear strength which is more than 13 N/mm2.
In the case of another embodiment of the optical cable, the optical cable has a diameter which is less than 6.5 mm. In a preferred embodiment of the optical cable, the optical cable has a diameter which is more than 3.5 mm.
In another configuration of the optical cable, the optical transmission element has several optic fibers, which are surrounded by a second sleeve. The second sleeve of the optical transmission element may be formed from a plastics material.
Another embodiment of the optical cable provides that the cable core is formed as a cable core without any filling compound.
In the case of a further configuration of the optical cable, the cable core has a centrally arranged yarn, around which the several optical transmission elements are arranged. The centrally arranged yarn may comprise a water-swellable material. The at least one yarn, which is arranged between the optical transmission elements and the first sleeve, and/or the centrally arranged yarn may be formed as a filament of polyester.
According to another embodiment of the optical cable, the swellable material contains an acrylate. The swellable material may also contain a salt of an acrylic acid.
A further embodiment of the optical cable provides that the cable jacket has at least two layers. In the case of one embodiment of the optical cable, a first of the at least two layers of the cable jacket, which is adjacent the first sleeve, contains polycarbonate. In the case of another embodiment of the optical cable, a first of the at least two layers of the cable jacket, which is adjacent the first sleeve, contains a polymer blend. In a preferred embodiment, a second of the at least two layers of the cable jacket, which is adjacent the first layer of the at least two layers of the cable jacket, contains high-density polyethylene. According to a development of the optical cable, a second of the at least two layers of the cable jacket, which is adjacent the first layer of at least two layers of the cable jacket, contains polyamide. In the case of a further configuration, a second of the at least two layers of the cable jacket, which is adjacent the first layer of the at least two layers of the cable jacket, contains polyurethane.
An optical cable which is formed according to the features specified above can be used with preference for blowing into an empty tube.
A method for the production of an optical cable envisages the provision of a cable core with several optical transmission elements, which respectively contain at least one optic fiber, at least one yarn being arranged around the several optical transmission elements, which yarn respectively contains a water-swellable material. The cable core is surrounded by the first sleeve, which contains a paper material. A cable jacket made from a plastics material is extruded around the first sleeve.
According to a development of the method, the strip is provided with a tear strength which is less than 16 N/mm2. In the case of another embodiment of the method, the strip is provided with a tear strength which is more than 13 N/mm2.
In the case of another embodiment of the method, the at least one optical transmission element is provided by several of the at least one optic fiber being arranged in a second sleeve, which contains a plastics material. In the case of a development of the method, the cable core is provided by several of the at least one optical transmission element being arranged around a yarn, which comprises a water-swellable material.
According to a further feature of the method, the cable core is provided as a cable core without any filling compound.
The strip made from the paper material is preferably formed into a first sleeve by means of a forming tube.
Another embodiment of the method provides that, when the cable jacket is extruded, a first layer of polycarbonate is extruded around the first sleeve and a second layer of high-density polyethylene is extruded around the first layer of the cable jacket.
Further embodiments concerning the optical cable and the method for the production of the optical cable can be taken from the subclaims.